Woodland and hedgerows

Lichen Diversity (Ellenberg Method)


Additional nitrogen supply both leads to a eutrophication of tree bark and changes in bark pH. In particular, enhanced levels of NH3 have been shown to increase bark pH. The environmental preferences of lichens in relation to these different conditions may be classified into two extremes: 'nitrophyte' lichen species prefer high supply of nitrogen and high bark pH, while 'acidophyte' lichen species prefer a low supply of nitrogen and the naturally low pH of clean bark.

Lichen Diversity (Lichens on twigs method)


Twigs provide a new substrate every year and colonising lichen communities are strongly affected by existing climatic and atmospheric conditions as well as by availability of propagules. Data on lichen diversity from a standard sampling procedure along woodland and or hedgerow margins allows a comparison of lichen communities in the vicinity of a range of environmental conditions, particularly those associated with agricultural conditions. The procedure is repeatable allowing an assessment of changes over time.

Lichen Diversity (Lallement)


This method was developed in France to provide a rapid assessment of air pollution particularly nitrogen over a large geographical area using 14 easily recognisable macro-lichen species associated with well defined phytosociological communities selected from the van Haluwyn and Lerond scale (1988). Land use in each unit was used as a basis for assessing nitrogen levels.

Lichen Acidophyte-Nitrophyte Diversity (Dutch method)


Lichen diversity and cover is assessed on trunks of specified trees and weighted according to selected species that are classified as "nitrophytes" (species preferring nitrogen enriched tree bark) or "acidophytes" (species preferring naturally acidic clean tree bark). The method was developed in the Netherlands based on large-scale monitoring in conjunction with physicochemical measurements (van Herk 1999, 2002).

Invertebrates responses


Insect pests: It is generally thought that the increased infestations of insect pests particularly sucking insects, observed following N addition from the atmosphere or as fertiliser, is a response to increased N content of the plants. While the presence of certain pests may indicate an effect of N deposition, their absence does not indicate the lack of an effect and the introduction of pests in order to observe change is not acceptable.

Frost Hardiness (Nitrogen)


The ability of plants to minimise the risk of freezing damage is conferred by sychronising their phenology with the growing environment. The indigenous flora generally has a good safety margin between its frost hardened status and minimum temperatures, unless the growth environment changes. A negative link between enhanced N deposition and reduced frost hardiness was widely suspected to be a casual factor in the observed decline of red spruce in the nineteen eighties (Eagar & Adams 1992).


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